The invention relates to matrix powders for the production of bodies or components for wear-resistant applications, and to a component produced therefrom.
Known matrix powders are processed using an infiltrant to form wear-resistant components which are used predominantly in the oil exploration sector.
A particular field of use for matrix powders is the production of diamond drill bits for oil drilling. As far as the applicants are aware, the relevant prior art is given in U.S. Pat. No. 5,733,664, U.S. Pat. No. 5,733,649 and U.S. Pat. No. 5,589,268.
In all three of the patents mentioned above, sintered crushed cermets, predominantly based on tungsten carbide with cobalt as binder metal, and monocrystalline tungsten carbide (WC) and cast tungsten carbide, a eutectic mixture of WC and W2C, are mentioned with regard to the hard materials for the compositions of the matrix powder.
In U.S. Pat. No. 5,733,664, in addition to sintered crushed cermets based on WC with cobalt as binder metal, sintered crushed cermets based on WC with nickel as metallic binder are also described.
According to all three patents, the particle sizes of the hard materials used are of the order of magnitude of 45 to 180 xcexcm or of the order of magnitude of 400 to 120 mesh; mixtures of various particle size fractions are mentioned, but overall these always lie in the range from 45 to 180 xcexcm or from 400 to 120 mesh. The matrix powders which are mentioned in the patent may contain either just one hard material component or mixtures of various hard materials.
U.S. Pat. No. 5,733,664 and U.S. Pat. No. 5,589,268 encompass not only the actual matrix powders but also the infiltration materials. These are alloys of composition Cuxe2x80x94Nixe2x80x94Zn and Cuxe2x80x94Mnxe2x80x94Nixe2x80x94Zn, in some cases also with additions of Mn, B and Si.
In a different technical field FR 2 667 804 describes a process for producing plates with a wear-resistant surface, in which the wear-resistant surface is formed by a composite material based on tungsten carbide powder bound in a soldering alloy. The tungsten carbide powder used in this case comprises cast tungsten carbide (WC-W2C), most of the particles being spherical in shape and having a diameter of more than 0.5 mm.
The various particle size ranges, which are matched to one another, of the individual hard materials used for the production of diamond drill bits in accordance with U.S. Pat. No. 5,733,664, U.S. Pat. No. 5,733,649 and U.S. Pat. No. 5,589,268 should provide not only a good resistance to abrasion but also a good resistance to erosion to the infiltration component subsequently produced therefrom. In practice, however, it has been found that the hard materials used, if the matrix surrounding them is washed out through erosion, offer a good point of attack for the wear-inducing material.
Furthermore, although these hard-material particles do have a very high hardness, they are also, by their very nature, very brittle. The associated reduced impact strength in turn makes it easier for fractures to form, in particular from corners and edges of block particles of these materials. Moreover, in addition to the notch effect for the surrounding matrix caused by the edged morphology of such hard materials, a further notch effect occurs when the hard materials fracture, which can cause additional incipient cracking in the surrounding matrix material. This incipient cracking or these initial cracks then have an adverse effect on the fatigue strength of the infiltrated component.
It is an object of the invention to provide a matrix powder and a wear-resistant component produced therefrom in which, compared to known matrix powders or components, the mechanical properties in use, in particular the resistance to erosion, are improved.
The invention is based on the discovery that the particle shapes of the hard material particles used have a disadvantageous effect with regard to the wear resistance of the infiltrated components with the abovementioned compositions for matrix powders. Their block and edged morphology means that they offer a good point of attack for the wear-inducing material.
The drawbacks in the wear resistance of previous infiltration components can be considerably alleviated by the use of spheroidal hard materials, since spheroidal particles, especially if they are in the same particle size range as the abrasive or erosive material, offer a substantially smaller surface for this material to attack.
Furthermore, spheroidal hard materials do not give rise to any notch effect into the surrounding matrix, with the result that the fatigue strength of infiltrated components is improved considerably. If spheroidal hard materials are made in the form of a dense-sintered composite, comprising metal carbides and a metallic binder, it is also possible to improve the impact strength of such hard-material particles compared to pure carbides, so that the above mentioned additional notch effect when the particles break can be reduced, which in turn results in an improved fatigue strength of the infiltration bodies.
Therefore, the invention relates to matrix powders which contain spheroidal hard materials, preferably in particle sizes of the same order of magnitude as the attacking wear-inducing particles. Components produced from these matrix powders exhibit improved mechanical properties.
The hard material particles used may firstly be spheroidal carbides, as described in U.S. Pat. No. 5,089,182 in the name of the present applicant. It is also possible to use dense-sintered spheroidal powders, preferably with a closed porosity or pore-free. Alternatively, it is also possible for the spheroidal hard materials to be in the form of sintered pellets, as are produced in accordance with the prior art by various manufacturers, such as Kennametal Inc., Latrobe, Reed Tool Company, Houston and also the assignee of the present invention.
A matrix powder according to the invention for the production of components for wear-resistant purposes which contain hard material in powder form is distinguished by the fact that at least some of the hard material is in the form of spheroidal hard-material particles with a particle size of less than 500 xcexcm. The particle size of the spheroidal hard materials is particularly preferably between 20 and 250 xcexcm.
It is possible for the matrix powder to consist exclusively of the spheroidal hard material. However, it is also possible to add further constituents to the matrix powder. The above mentioned advantageous properties of the matrix powder and the infiltration components manufactured therefrom can be observed even if only at least 5% by weight of the matrix powder is formed by spheroidal hard-material particles. However, it is preferable for at least 30% by weight of the matrix powder to be formed from spheroidal hard-material particles, and even more than 50% by weight is particularly preferred.
To allow infiltration of the matrix powder during production of a component which is to be protected against wear, it may be of assistance for the matrix powder to contain a further component which functions as a spacer, so that, in particular with small particle sizes, the spheroidal hard-material particles are not packed too closely together. In such cases, the matrix powder may contain block hard material, e.g. in the form of crushed carbides, or a metal powder. When using block carbides, the particle size of these carbides is preferably between 3 and 250 xcexcm. The particle size of a metallic powder used is preferably between 20 and 150 xcexcm. Examples of the metallic powders and block hard materials which can be used and of the spheroidal hard materials are given in the exemplary embodiments.